In recent years, toners have been desired to have small particles size and hot offset resistance for giving high quality output images, low temperature fixing ability for energy saving, and heat resistant storage stability for resisting high-temperature, high-humidity environments during storage or transport after production. Particularly, low temperature fixing ability is very important quality of a toner, as power consumption for fixing occupies a large part in the power consumption for an entire image forming process.
Conventionally, toners produced by a kneading and pulverizing method have been used. The toner produced by the kneading and pulverizing method have problems that it is difficult to reduce the particle size thereof, and shapes of particles are uneven and a particle diameter distribution thereof is broad, which result in unsatisfactory quality of output images, and a large quantity of energy is required for fixing such toner. In the case where wax (i.e., a releasing agent) is added to the toner for improving fixing ability, moreover, the toner produced by the kneading and pulverizing method contains a large amount of the wax present near toner surfaces, as a kneaded product is cracked from an interface of wax during pulverizing. As a result of this, a releasing effect is exhibited, but on the other hand, the toner tends to cause toner deposition (i.e., filming) on a carrier, a photoconductor, and a blade. Therefore, such toner is not satisfactory in view of its characteristics on the whole.
To encounter the aforementioned problems associated with the kneading and pulverizing method, a production method of a toner in accordance with a polymerization method has been proposed. A toner produced by the polymerization method is easily produced as small particles, has a sharp particle diameter distribution compared to that of the toner produced by the pulverizing method, and can encapsulate a releasing agent therein. As a production method of a toner in accordance with the polymerization method, proposed is a method for producing a toner using an elongation reaction product of urethane-modified polyester as a toner binder, for the purpose of improving low temperature fixing ability, and hot offset resistance (see PTL 1).
Moreover, proposed is a production method of a toner, which is excellent in all of heat resistant storage stability, low temperature fixing ability, and hot offset resistance, as well as excellent in powder flowability and transfer ability, when a toner is produced as a small-diameter toner (see PTLs 2 and 3).
Further, disclosed is a production method of a toner having a maturing step for producing a toner binder having a stable molecular weight distribution, and achieving both low temperature fixing ability and (see PTLs 4 and 5).
However, these proposed techniques do not provide a toner having a high level of low temperature fixing ability, which has been demanded in recent years.
For the purpose of achieving a high level of low temperature fixing ability, therefore, proposed is a toner containing a resin including a crystalline polyester resin, and a releasing agent, and having a phase separation structure, where the resin and the releasing agent (e.g., wax) are incompatible to each other in the form of sea-islands (see PTL 6).
Moreover, proposed is a toner containing a crystalline polyester resin, a releasing agent, and a graft polymer (see PTL 7).
These proposed techniques can achieve low temperature fixing, as the crystalline polyester resin is rapidly melted, compared to a non-crystalline polyester resin. The proposed toners can have desired low temperature fixing ability and desired heat resistant storage stability at the same time, but have a problem when used in a high-speed apparatus that increased stress applied to the toner will form aggregates of the toner particles, and cause a cleaning doctor clog to form white voids (white voids after transfer) of the toner on output toner images. Moreover, in the case of toners containing a crystalline polyester resin, they have a problem of forming aggregates of the toner particles in high-temperature, high-humidity environments.
Accordingly, there has been a need to provide a high-quality toner that has desired low temperature fixing ability and desired heat resistant storage stability at the same time, and can prevent formation of white voids after transfer.